This invention relates in general to vehicle axle assemblies and in particular to an improved structure for a housing for such an axle assembly and a method for manufacturing same.
Axle assemblies are well known structures which are in common use in most vehicles. Such axle assemblies include a number of rotatable components which transmit rotational power from an engine of the vehicle to the wheels thereof. These rotatable components are usually enclosed in protective non-rotatable housing. The housing typically includes a central carrier (which rotatably supports a differential mechanism therein) having a pair of outwardly extending tubes (which enclose the axle shafts extending from the differential to the wheels of the vehicle). In the past, the tubes have been formed from sections of hollow cylindrical steel tubes which have been welded, bolted, or otherwise secured to the carrier to form the axle housing.
The tubes of these axle housings are frequently provided with one or more additional components for various purposes. For example, it is generally desirable to provide a circumferentially extending flange about the tube near the outer end thereof to function as a mounting surface for the components of the brake for that wheel. Also, a seat is commonly provided on the tube for securing a plurality of leaf springs or similar means for resiliently connecting the frame of the vehicle to the axle housing. Lastly, it is known to provide a pad on the tube to which a bracket is welded for securing a shock absorber or similar means for dampening oscillations of the frame of the vehicle relative to the axle housing. In the past, the brake flange, the spring seat, and the shock absorber pad have all been formed from individual components which were welded, bolted, or otherwise secured to the tubes.
More recently, it has been found desirable to form the axle housing integrally by casting molten metal into an appropriately shaped mold. Thus, it is known to form the carrier and tubes of the axle housing from a single piece of material cast into a predetermined shape. Furthermore, it has also been found desirable to form the additional components of the axle housing (i.e., the brake flange, the spring seat, and the shock absorber pad) integrally with the tubes by casting. Known axle housing castings have been formed from nodular graphite iron material.
However, known axle housing castings have followed traditional thinking regarding the structures of the tubes. Specifically, the tubes of such known castings have been formed having uniform wall thicknesses, similar to the sections of hollow cylindrical steel tubing which were connected to the carriers of prior axle housings. However, it has been found that some portions of the axle housing tubes are subjected to relatively large stresses during operation, while other portions of the axle housing tubes are subjected only to relatively small stresses. In prior axle housings using a uniform wall thickness tube, the thickness of the tube was selected to accommodate the maximum stress applied at any point thereon. As a result, the remainder of the tube was over-designed for its intended use. In other words, the amount of material used to form the remainder of the tube was much larger than the amount required to prevent failure.
Thus, it can be seen that known axle housing castings are inefficient because they are composed of more material than is required to accomplish the intended function. The inclusion of the additional material in the known axle housing castings results in unnecessary material cost and increased weight. Since cost and weight are prime considerations in the design of axle housings and other vehicle components, it would be desirable to provide an improved axle housing casting which meets its intended functional requirements without adding unnecessary cost or weight thereto.